Importance:American Heart Association guidelines recommend echocardiography in Kawasaki disease at baseline, 1 to 2 weeks, and 4 to 6 weeks after treatment to detect coronary artery abnormalities. However, these examinations are expensive and may require sedation in young children, which is burdensome and carries some risk. Objective:To assess the benefit of additional echocardiographic imaging at 6 weeks in patients with uncomplicated Kawasaki disease who had previously normal coronary arteries. Design, Setting, and Participants:This is a retrospective review of patients with Kawasaki disease who were cared for between 1995 and 2014 in 2 academic pediatric referral practices Eligibility criteria included receiving intravenous immunoglobulin treatment for acute Kawasaki disease at a center; the absence of significant congenital heart disease; available echocardiographic measurements of both the right and left anterior descending coronary arteries at 10 days or less after diagnosis (baseline), 2 (±1) weeks, and 6 (±3) weeks of illness; and normal coronary arteries at baseline and 2 weeks, defined as maximum coronary artery z scores less than 2.0 and no distal aneurysms. Data analysis was completed from March 2015 to November 2015. Main Outcomes and Measures:The number of patients with right coronary artery or left anterior descending coronary artery z scores of 2.0 or more at 6 weeks. Results:The median age of the 464 included patients was 3.3 years (interquartile range, 1.8-5.4 years); 264 (56.9%) were male, 351 of 414 for whom data were available (84.8%) had complete Kawasaki disease, and 66 (14.2%) received additional intravenous immunoglobulin treatment. At 6 weeks of illness, 456 patients (98.3%) who had had normal coronary artery z scores at baseline and 2 weeks continued to have normal z scores. Of the remaining 8 patients (1.7%), the maximum z score within 6 weeks was 2.0 to 2.4 in 5 patients (1.2%), 2.5 to 2.9 in 1 patient (0.2%), and 3.0 or more in 2 patients (0.4% [95% CI, 0.1%-1.5%]). Coronary artery dimensions ultimately normalized in all but 1 patient, who had minimal dilation at 6 weeks (right coronary artery z score, 2.1). Sensitivity analyses using less restrictive cut points (eg, a maximum z score <2.5) or less restrictive timing windows (eg, considering patients with incomplete echocardiographic data within 21 days) gave similar results; in these analyses, 454 to 463 of 464 patients (98% to 99.7%) had coronary artery z scores of less than 2.5 at 6 weeks. Conclusions and Relevance:New abnormalities in coronary arteries are rarely detected at 6 weeks in patients with Kawasaki disease who have normal measurements at baseline and 2 weeks of illness, suggesting that the 6-week echocardiographic imaging may be unnecessary in patients with uncomplicated Kawasaki disease and z scores less than 2.0 in the first 2 weeks of illness.